CD8⁺ T lymphocytes in the peripheral airways have been suggested to be involved in the pathogenesis of COPD. However, the significance of CD8⁺ T lymphocyte activation in COPD is not well understood. A biomarker of CD8⁺ T lymphocyte activation in patients with COPD is required.

Thirty COPD patients and twenty-one healthy controls (eleven ex-smokers and ten who had never smoked or were light ex-smokers) were included in this study. We separately obtained epithelial lining fluid (ELF) from central and peripheral airways using a bronchoscopic microsampling technique. Levels of perforin in ELF were measured and we examined correlations between its values and patients characteristics including pulmonary function.

Perforin levels in both the central and peripheral airways in COPD patients were significantly higher than those in the healthy control groups. In the healthy control groups, there was no significant difference in perforin levels between central and peripheral airways. However, in COPD patients, perforin levels in peripheral airways were significantly higher than those in central airways. Perforin levels in peripheral airways were significantly correlated with FEV₁ (percent predicted), FEV₁/FVC, and DLco (percent predicted) in COPD patients.

The microsampling technique is safe and useful for separately obtaining ELF from central and peripheral airways. Levels of perforin in ELF from peripheral airways were significantly increased and correlated with the degree of pulmonary dysfunction. Perforin might reflect inflammation involving CD8⁺ T-lymphocytes. This novel biomarker might enable better understanding of the pathogenesis of COPD.